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Simplify codegen for is-expressions #65845

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Simplify codegen for is-expressions #65845

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14 changes: 10 additions & 4 deletions src/Compilers/CSharp/Portable/BoundTree/BoundDecisionDag.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -84,7 +84,7 @@ public ImmutableArray<BoundDecisionDagNode> TopologicallySortedNodes
/// takes as its input the node to be rewritten and a function that returns the previously computed
/// rewritten node for successor nodes.
/// </summary>
public BoundDecisionDag Rewrite(Func<BoundDecisionDagNode, IReadOnlyDictionary<BoundDecisionDagNode, BoundDecisionDagNode>, BoundDecisionDagNode> makeReplacement)
public T Rewrite<T>(Func<BoundDecisionDagNode, IReadOnlyDictionary<BoundDecisionDagNode, T>, T> makeReplacement)
{
// First, we topologically sort the nodes of the dag so that we can translate the nodes bottom-up.
// This will avoid overflowing the compiler's runtime stack which would occur for a large switch
Expand All @@ -93,20 +93,26 @@ public BoundDecisionDag Rewrite(Func<BoundDecisionDagNode, IReadOnlyDictionary<B

// Cache simplified/translated replacement for each translated dag node. Since we always visit
// a node's successors before the node, the replacement should always be in the cache when we need it.
var replacement = PooledDictionary<BoundDecisionDagNode, BoundDecisionDagNode>.GetInstance();
var replacement = PooledDictionary<BoundDecisionDagNode, T>.GetInstance();

// Loop backwards through the topologically sorted nodes to translate them, so that we always visit a node after its successors
for (int i = sortedNodes.Length - 1; i >= 0; i--)
{
BoundDecisionDagNode node = sortedNodes[i];
Debug.Assert(!replacement.ContainsKey(node));
BoundDecisionDagNode newNode = makeReplacement(node, replacement);
T newNode = makeReplacement(node, replacement);
replacement.Add(node, newNode);
}

// Return the computed replacement root node
var newRoot = replacement[this.RootNode];
var result = replacement[this.RootNode];
replacement.Free();
return result;
}

public BoundDecisionDag Rewrite(Func<BoundDecisionDagNode, IReadOnlyDictionary<BoundDecisionDagNode, BoundDecisionDagNode>, BoundDecisionDagNode> makeReplacement)
{
var newRoot = Rewrite<BoundDecisionDagNode>(makeReplacement);
return this.Update(newRoot);
}

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